Chromium electroplating began in the late 19th or early 20th century and provides a superior functional surface coating with respect to both wear and corrosion resistance. However, in the past, this superior coating, as a functional coating (as opposed to a decorative coating), has only been obtained from hexavalent chromium electroplating baths. Chromium electrodeposited from hexavalent chromium baths is deposited in a crystalline form, which is highly desirable. Amorphous forms of chromium plate are not useful for functional applications. The chemistry used in the conventional technology is based on hexavalent chromium ions, which are considered carcinogenic and known to be toxic. Hexavalent chromium plating operations are subject to strict and severe environmental limitations. While industry has developed many methods of working with hexavalent chromium to reduce the hazards, both industry and academia have for many years searched for a suitable alternative. The most often sought alternative has been trivalent chromium. Until the present inventor's recent successes, the efforts to obtain a dependable, reliable functional chromium deposit based on a trivalent chromium process has continued without success for over one hundred years. Additional discussion of the need for a replacement for hexavalent chromium is included in the earlier application related to the present assignee's efforts in the area of chromium deposits from trivalent chromium, published as WO 2007/115030, the disclosure of which is hereby incorporated herein by reference.
As is apparent from the plethora of prior art attempts to obtain a functional crystalline chromium deposit from trivalent chromium, there has long been ample motivation to seek this goal. However, as is equally apparent, this goal has been elusive and, prior to the present invention, has not been attained in the prior art, despite quite literally a hundred years of trying.
For all these reasons, a long-felt need has remained unmet for (1) a crystalline-as-deposited functional chromium deposit, (2) an electrodeposition bath and process capable of forming such a functional chromium deposit, and (3) articles made with such a functional chromium deposit, in which the crystalline chromium deposit is free of macrocracks and is capable of providing the desired functional wear and corrosion resistance characteristics comparable to the conventional functional hard chromium deposit obtained from a hexavalent chromium electrodeposition process. The urgent need for a bath and process capable of providing a crystalline functional chromium deposit from a bath substantially free of hexavalent chromium heretofore has not been satisfied prior to the present invention and the present inventor's previous efforts as disclosed in WO 2007/115030.